Benefits
Higher muscle protein synthesis than leucine in one 10-man trial
In a crossover trial, 10 healthy young men took 2 g of dileucine or 2 g of leucine on separate occasions. Cumulative myofibrillar protein synthesis over 3 hours rose with dileucine (0.075 %/h) but not with leucine (0.047 %/h, p=0.023), a difference of about 60% between the two means. Two limits matter. Plasma leucine exposure was the same after both drinks (p=0.396), so the extra synthesis was not explained by more leucine reaching the blood. And a protein synthesis rate measured in a muscle biopsy is a laboratory endpoint, not a gain in muscle size or strength. Ten participants, and the trial was funded by the company that developed the ingredient.
One leg press measure improved over 10 weeks
Thirty-four resistance-trained men, roughly 11 per group, trained 4 days a week for 10 weeks while taking 2 g/day of dileucine, 2 g/day of leucine or placebo. Leg press one-rep max increased more with dileucine than with placebo (p=0.02), and leg press reps to failure increased more with dileucine than with leucine (p=0.04). Nothing else separated the groups: bench press strength and endurance, body composition, anaerobic capacity, countermovement jump and maximal voluntary contraction all showed no group difference. The confidence interval on the leg press strength result was wide, from 5.8 to 73.2 kg, the groups were small, and the study was sponsored by the company that supplies the ingredient.
Muscle breakdown was measured and was not reduced
Two human dileucine trials measured muscle protein breakdown directly and neither found a reduction. In the 10-man crossover trial, mixed muscle protein breakdown was 0.043 %/h after leucine and 0.051 %/h after dileucine, with no difference between them (p=0.659). In the post-exercise trial, urinary 3-methylhistidine, a marker of myofibrillar breakdown, did not differ between a dileucine-containing amino acid drink, a BCAA drink and collagen (p=0.58). No trial has tested dileucine during dieting or caloric restriction, so there is no human evidence that it preserves muscle in a cut.
Not tested in older adults
Every published dileucine trial recruited young adults: 10 men averaging 23 years, 34 resistance-trained men averaging 28 years, and 12 recreationally active adults averaging 24 years. No trial has enrolled older adults, and none has measured muscle mass, strength or physical function in an older population. The absorption argument is a mechanism, not a result, and it has not been tested in aging muscle.
Mechanism of action
PEPT1 dipeptide transporter absorption
Free leucine crosses the intestinal brush border on amino acid carriers, chiefly B0AT1, while dipeptides use PEPT1, a separate proton-coupled peptide transporter. Dileucine does reach the blood intact: plasma dileucine rose further after dileucine than after leucine (p=0.013) in the 10-man crossover trial. What that trial did not show is more leucine in the blood, because plasma leucine exposure was the same after both drinks (p=0.396). PEPT1 is itself saturable, so this route has a ceiling too.
mTORC1 signalling: no measured difference from leucine
The 10-man crossover trial took muscle biopsies and measured mTORC1 signalling directly. Akt, rpS6 and p70S6K phosphorylation rose over time after leucine and after dileucine alike, with no separation between conditions, and 4E-BP1 phosphorylation did not change after either (p=0.229). The cell-culture arm of the 2025 trial also found no effect on p-RPS6 (p=0.39) or p-4E-BP1 (p=0.50). So the higher synthesis rate seen with dileucine was not matched by a stronger measured mTORC1 signal, and the mechanism is not yet explained.
Clinical trials
Hagele AM et al., PLoS One 2024 (NCT06121869, registered retrospectively). Randomized, double-blind, placebo-controlled trial in 34 resistance-trained men taking 2 g/day dileucine monohydrate, 2 g/day leucine or placebo alongside a 4-day-per-week training programme for 10 weeks. Outcomes measured: leg press and bench press one-rep max and reps to failure, body composition, anaerobic capacity, countermovement jump, maximal voluntary contraction. Muscle protein synthesis was not measured. The material tested was branded RAMPS at the time and is the same dileucine now sold as DL-185; the sponsor was its developer, Ingenious Ingredients LP.
34 resistance-trained men, average age 28, about 11 per group. No women, no untrained people, no older adults.
Leg press one-rep max rose more with dileucine than with placebo (p=0.02; 95% CI 5.8 to 73.2 kg) and leg press reps to failure rose more with dileucine than with leucine (p=0.04). Every other comparison was null: bench press one-rep max and reps to failure, body composition, anaerobic capacity, countermovement jump and maximal voluntary contraction showed no group differences. Leucine beat neither placebo nor dileucine on any measure. One small sponsor-funded trial with about 11 men per group, with no independent replication.